1. Field of the Invention
The present invention relates to a method for producing an arc tube for a discharge lamp device. More particularly, the invention relates to a method for producing an arc tube wherein a novel guide pipe and pushing member may be used to facilitate insertion of the electrode assembly into the glass tube of the arc tube.
2. Description of the Related Art
As shown in FIG. 9, an arc tube for a discharge lamp device has a structure in which a sealed chamber portion 5a, in which electrode rods 6 are opposed to each other and a light emitting substance and the like are hermetically enclosed, is formed between a pair of front and rear pinch seal portions 5b. An electrode assembly A or A′ is sealingly attached to each of the pinch seal portions 5b to ensure the gas-tightness of the sealed chamber portion 5a. In the electrode assembly, the electrode rod 6 which is protruded into the sealed chamber portion 5a, a lead wire 8 which is led from the pinch seal portion 5b, and a molybdenum foil 7 through which the rod 6 and the wire 8 are connected to each other are connected and integrated to one another.
The arc tube 5 is produced by the following method. As shown in FIG. 10A, first, the electrode assembly A, in which the electrode rod 6, the molybdenum foil 7, and the lead wire 8 are connected and integrated to one another, is inserted into a cylindrical glass tube W from the side of one open end. In the glass tube, a chamber portion w2 is formed in a middle of a linear elongated portion w1. A position q1 in the vicinity of the chamber portion w2 is first-pinch-sealed. As shown in FIG. 10B, thereafter, a light emitting substance P and the like are introduced into the chamber portion w2 from the side of the other open end, and, as shown in FIG. 10C, the other electrode assembly A′ (see FIG. 11) in which a bent portion 8a is formed in the lead wire 8 is then inserted into the glass tube to be self-held thereinto. Specifically, in the electrode assembly A′ inserted into the glass tube W, the bent portion 8a, having a width which is larger than the inner diameter of the glass tube W, is formed in the lead wire 8. The bent portion 8a pressingly contacts with the inner peripheral face of the glass tube W. The electrode assembly is self-held by the force due to the press contact to the position where the electrode assembly is inserted. Thereafter, the other open end of the glass tube W is provisionally sealed using burners. The portion of the glass tube W where the electrode assembly A′ is inserted is second-pinch-sealed, and the glass tube W is cut at a predetermined position on the side of the provisional sealing to expose the lead wire 8 from the glass tube W.
Preferably, the articles in (the chamber portion of) the arc tube are enclosed without being contaminated as a result of contact with the atmosphere. Therefore, the steps from the step of charging of the light emitting substance P and the like to that of provisional sealing are conducted in the form where, as shown in FIG. 12, an upper open end portion of the glass tube W is fixedly held to a cylindrical connection head 2 disposed in a glove box 1 which is filled with argon gas, and the glass tube W communicates with the glove box 1. In the step of inserting the electrode assembly A′ into the glass tube W, the electrode assembly A′ is held by a holding chuck 4 of a holding member 3, and the electrode assembly is then inserted into the glass tube W through a hole 2a of the connection head 2.
In the step of inserting the electrode assembly A′, it is required to correctly insert the electrode assembly A′ on the second-pinch-seal side into the glass tube W so that the electrode assembly A′ is positioned symmetrically with the electrode assembly A on the first-pinch-seal side. However, the connection head 2 has an axially elongated shape in which vent holes and portions for fixing with the glove box are formed, the hole 2a of the connection head 2 is narrow, and the chamber portion w2 is located at a considerably lower position. Therefore, the holding chuck 4 is so thin that the force of holding the electrode assembly A′ is insufficiently exerted. As a result, there arises a problem in that it is difficult to correctly insert the electrode assembly A′ to an adequate position, or particularly so that the position of the molybdenum foil 7 coincides circumferentially with that of the molybdenum foil on the first-pinch-seal side.
In order to solve the aforementioned problem, the inventor of the present invention conceived the following configuration. As shown in FIGS. 13A and 13B, a funnel-like guide pipe 9 having a hole which is equal in inner diameter to the hole of the glass tube W is attached to the hole 2a of the connection head 2 from the upper side. The electrode assembly A′ is inserted into the guide pipe 9 from the upper side, thereby causing the electrode assembly A′ to be once self-held into the guide pipe 9 by the pressure contact force which is exerted by the bent portion 8a of the lead wire 8 on the pipe wall. Thereafter, the electrode assembly A′ is pushed by a thin rod-like pushing member 9a to be advanced to a predetermined position in the glass tube W. As a result, the dimensional restriction of the holding chuck 4 (the restriction that the holding chuck must be thin and long) is eliminated, and an adequate force required for holding the electrode assembly A′ can be ensured. Preferably, the guide pipe 9 is made of a material which hardly introduces pollutants into the glove box 1. One such material is stainless steel, which has excellent rustproofness and is washable.
In this configuration, unlike the related art, it is not necessary for the holding chuck 4 to have a thin shape which enables the holding chuck to be deeply inserted into the glass tube W, rather, the holding chuck 4 is required only to have a function of allowing the electrode assembly A′ into the guide pipe 9. Therefore, it was confirmed that a sufficient force of holding the electrode assembly A′ can be ensured even when the holding chuck is reduced in length and increased in thickness.
In an arc tube produced by the above-described method in which the electrode assembly A′ is inserted into the glass tube W via the guide pipe 9, however, there arose new problems of a flickering phenomenon, an abnormal emission color, and an insufficient luminous flux. The present inventor searched for a cause of these problems, and found the following phenomenon. When the electrode assembly A′ is pushed into the glass tube W via the guide pipe 9, the inner peripheral face of the stainless steel guide pipe 9 is rubbed with the bent portion 8a of the molybdenum lead wire 8 to be shaved off, and shaved stainless steel chips in the form of powder drop into the chamber portion w2. The stainless steel powder is enclosed in the chamber portion w2 as a result of the second pinch seal. Therefore, stainless steel powder which should not exist in the chamber portion w2 exists as a foreign matter in the portion, causing a flickering phenomenon, an abnormal emission color, an insufficient luminous flux, etc.
In order to prevent the phenomenon from occurring, the inventor conceived a configuration in which a longitudinal groove is formed in the inner side of the guide pipe 9, and the groove is to be axially engaged with the bent portion 8a of the lead wire of the electrode assembly A′ to rotationally lock the bent portion 8a, whereby (the bent portion 8a of) the electrode assembly A′ is prevented from being in sliding contact with the guide pipe 9 when the electrode assembly A′ is pushed into the glass tube W via the guide pipe 9. The inventor repeated experiments, and finally found that the configuration is effective in preventing the problems from occurring, thereby accomplishing the present invention.
The invention has been conducted in view of the problems of the related art and additional findings by the inventor. It is an object of the invention to provide a method of producing an arc tube for a discharge lamp device in which, when an electrode assembly on the second-pinch-seal side is to be inserted into a glass tube, the electrode assembly can be inserted correctly and smoothly to a predetermined position in the glass tube without being in sliding contact with a guide pipe.